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Claudia Lugo Posted: Jul 31, 2008 02:18 PM	New and out of my element. I've just started adminstrating this business and boss has asked me to become informed on some generalities. I've done some reading but have a question about r-ratings. I understand that the thickness of foam dictates the r-rating for insulation. But I believe that the r-rating grows exponentially, and not in direct relation with the thickness of the layer. So if a 1 inch layer is applied, the R-rating is about 6 or 7. What is the rating for 2 inches? How is this calculated? Where can I find a table or chart that would help?
mason Posted: Jul 31, 2008 03:48 PM	Manufacturers are required to list the aged R value of the foam based on 1 inch. However, some manufacturers have aged R values for greater thickness. Normally you can multiply the R value at one inch by the total foam thickness to obtain a conservative estimate of total R value of the insulation. In some cases, the thicker the application the higher the R value per inch. Reason: SPF loses some of its initial R value over time (90% of the reduction is in the first 180 days after installation) This is due to outside air infiltrating into the exterior foam layers. The thickner the foam the less outside air goes into the foam, therefore the higher the aged R value. For more information check out my article on R values at my website, masonknowles.com
Claudia Lugo Posted: Aug 18, 2008 04:44 PM	Mason, Thank you so much for your help. I've read the article you referred me to and it was a great benefit. I think I've got the basics now, and then some! Thank you again, Claudia

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Claudia Lugo

Posted: Jul 31, 2008 02:18 PM

New and out of my element.

I've just started adminstrating this business and boss has asked me to become informed on some generalities. I've done some reading but have a question about r-ratings.

I understand that the thickness of foam dictates the r-rating for insulation. But I believe that the r-rating grows exponentially, and not in direct relation with the thickness of the layer.

So if a 1 inch layer is applied, the R-rating is about 6 or 7. What is the rating for 2 inches? How is this calculated? Where can I find a table or chart that would help?

mason

Posted: Jul 31, 2008 03:48 PM

Manufacturers are required to list the aged R value of the foam based on 1 inch. However, some manufacturers have aged R values for greater thickness.

Normally you can multiply the R value at one inch by the total foam thickness to obtain a conservative estimate of total R value of the insulation.

In some cases, the thicker the application the higher the R value per inch. Reason: SPF loses some of its initial R value over time (90% of the reduction is in the first 180 days after installation)

This is due to outside air infiltrating into the exterior foam layers. The thickner the foam the less outside air goes into the foam, therefore the higher the aged R value.

For more information check out my article on R values at my website, masonknowles.com

Claudia Lugo

Posted: Aug 18, 2008 04:44 PM

Mason,
Thank you so much for your help. I've read the article you referred me to and it was a great benefit. I think I've got the basics now, and then some!

Thank you again,
Claudia

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